Project

Sawtooth Passive Solar (New Zealand)

The Coatesville Passive Solar House in New Zealand, is capped by a series of stacking sawtooth roofs designed to capture every bit of sunlight during winter and naturally exhaust warm air through clerestories during summer. This 2,906 square foot (270 square meters) is situated on 1.5 acres in Rodney, North of Auckland, with bush and valley views. It is designed to be energy self-sufficient using a combination of passive solar, passive cooling, energy efficient technologies and a 4 kW solar panel system.

Typically, a passive solar house works on an east-west axis following the seasonal sunpath direction. Because the Coatesville house site sits a narrow, flat site located on the downward side of a hill, architect Duncan Firth of Solarei had to design within a restricted footprint that works on both an east-to-west axis and north-to-south axis for maximized solar gain and view. The sawtooth roof was the logical design approach.

The house relies on exposed insulated concrete slabs and large insulated vertical precast concrete walls for optimized passive solar gain and heating during winter. The roof shapes and clerestory windows allow a natural stack effect to cool the interior and naturally ventilate the bedrooms and living spaces over summer time.

As of November 2015, the house has thermally performed as calculated and intended. Internal temperatures passively peak at 24 degrees C during later afternoon mid-winter, with the extreme low at 17 degrees C during early morning. The house is designed for an anticipated 3800kWh’s annually or an annual energy index of 14.8kWh per/m2. The remaining power will eventually be provided by a 4kW grid-connected solar panel system.

Other incorporated green technologies and features include:

An on-site tiger worm composting system that treats blackwater and graywate

Domestic hot water is heated through a hot water heat pump (sucks heat out of the air)

A rainwater harvesting system that can provide 54,000 liters of potable water

Bio-paints on interior surfaces

Above-code insulation for walls and roof

Long,-lasting low maintenance natural bricks for the exterior

Cedar fascia boards at roof and deck edges

Energy-efficient appliances are standard items

Water conserving faucets in bathrooms and kitchen

Firth and Solarei specialize in environmental architecture, practicing in New Zealand, Southeast Asia and the United States.